1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly to a method of forming a metal interconnection line for a semiconductor device by using a contact plug.
2. Description of the Related Art
Generally, with high integration of semiconductor devices, pitch between metal interconnection lines and area of a contact hole are decreased, and aspect ratio is increased. In the case of metal interconnection line formed by using the sputtering technique, the strength of a coating for the metal wiring can become weakened. Accordingly, the metal interconnection line can short-circuit. In addition, as the depth of a diffusion region becomes shallower, a contact resistance of the metal interconnection line is increased. In order to solve these problems, the failure of the metal interconnection line is prevented and the contact resistance is reduced by forming a contact plug according to the prior art.
FIG. 1 is a sectional view of a conventional semiconductor device, showing a metal interconnection line structure employing a contact plug.
As shown in FIG. 1, an insulating layer 3 is formed on a semiconductor substrate 1 having an impurity region 2 formed therein. A portion of the insulating layer 3 is then etched to form a contact hole. Afterwards, a Ti/TiN film 4 acting as a barrier metal film is formed on upper surface and sides of the contact hole and on the insulating film 3. A contact plug 5 is formed within the contact hole with the Ti/TiN film 4. An aluminum alloy film 6 is formed on the Ti/TiN film 4 and the contact plug 5, and thus, the formation of the metal wiring is completed.
In the formation of the above metal interconnection line, the contact plug 5 is formed by depositing a tungsten(W) film on the Ti/TiN film 4 in order to fill the contact hole and by etching-back the tungsten film in order to expose the Ti/TiN film 4. At this time, in order to minimize the loss of the Ti/TiN film 4 which is positioned below the tungsten film at the time that the wolfram film is etched, end pointing etching is performed. Thereafter, an over etching is performed in order to completely remove the wolfram film remaining on the upper surface of the Ti/TiN film 4. If the over etching is not performed, the metal interconnection line is bridged by the remaining tungsten film. When the over etching is performed, however, a shallow groove is formed in the center of the upper surface of the contact plug 5 due to a high etching ratio of the tungsten film and the Ti/TiN film 4, and as a result, the metal interconnection line can short-circuit. When the metal interconnection line is formed within the contact hole by using the Ti/TiN film 4 and the tungsten film, the resistance of the metal interconnection line in the contact hole is increased because the resistance of the tungsten is greater than that of the aluminum. That is, the resistance of the wolfram is about 6 to 15.mu..OMEGA..circle-solid.cm, and the resistance of the aluminum is about 2.7 to 3.0.mu..OMEGA..circle-solid.cm. Accordingly, the resistance of the metal interconnection line is increased 2 to 10 times.